The present invention relates to an expansion valve provided in a refrigerant circuit of a refrigerating apparatus, air conditioner or the like and employed as a pressure reducing device for controlling the flow rate of a refrigerant.
As the pressure reducing devices for controlling the refrigerant flow rate in such a refrigerant circuit, a capillary tube and a thermostatic expansion valve are generally employed.
The capillary tube, which is adapted to regulate the refrigerant flow rate by means of the resistance of the passage in a tube having a very small bore, is suitable for use in a refrigerant circuit in which the condensing pressure and the evaporating pressure will not largely vary from the respective design points. In a refrigerant circuit in which such operating conditions largely change, however, the capillary tube cannot properly control the refrigerant flow rate, disadvantageously resulting in an excessive superheating of the refrigerant or liquid back to offer adverse effects to the refrigerant circuit or compressor.
On the other hand, the thermostatic expansion valve of the type disclosed in, for example, Japanese patent publication No. 9434/1978, represents a pressure reducing device which controls the refrigerant flow rate by sensing the temperature of a refrigerant circulating through a refrigerant circuit and controlling the valve opening in accordance with the sensed temperature.
The thermostatic expansion valve has a refrigerant inlet passage to be connected to the high-pressure side of a refrigerant circuit, a refrigerant outlet passage to be connected to the low-pressure side of the refrigerant circuit, and a valve seat as well as valve chest providing communication between both the passages. Further, a heat-sensitive bulb charged with a gas or liquid whose pressure varies with temperature, e.g., a refrigerant is connected to and opened into a diaphragm chamber through a tube of small diameter. To a diaphragm in the diaphragm chamber, the upper end of a valve stem is fixed, and a conical valve body facing the valve seat is provided on the lower end of the valve stem.
The heat-sensitive bulb is attached to an outlet conduit of an evaporator and is adapted to transmit a pressure corresponding to the temperature of the refrigerant circulating through the conduit to the diaphragm chamber through the tube of small diameter to transform the diaphragm by means of the transmitted pressure. This operation of the diaphragm causes the valve body to move through the valve stem to vary the degree of the opening in the valve seat portion, thereby to control the refrigerant flow rate.
However, such a thermostatic expansion valve also has a limit in transformation (valve lift) of the diaphragm; hence, it is difficult for the valve to effect the flow rate control over a wide range.
The above-mentioned prior art has also disclosed that a controllable flow rate range is enlarged by modifying the shape of the valve body, thereby to meet the demand for a flow rate control over a wider range.
More specifically, the valve body provided on the lower end of the valve stem is formed having a curved sealing surface, thereby increasing a maximum controllable flow rate. This method is, however, still insufficient for enlarging the controllable flow rate range, so that it is unfavorably impossible to allow a refrigerating apparatus or the like to exhibit its performance thoroughly.